In the recent years, optical discs have come into widespread use as a recording medium suitable for distribution, duplicate and retention of a large volume of data. Of these optical discs, a CD-format read only disc (CD-ROM), a recordable disc (CD-R) and a rewritable disc (CD-RW) constitute the most widespread optical disc family. A feature of the CD-ROM, CD-R and CD-RW pertaining to a CD family is an attribution of data thereof, with they being used properly on the basis of the data attributions.
The CD-ROM disc is of a type suitable for use in transferring data onto a substrate in the form of dented pits for duplicating the data with the same contents in large numbers. On the other hand, the CD-R or CD-RW is of a type permitting arbitrary additional recording or rewrite of data, and is thus suitable for data retention or the like at private levels. Of these, the CD-RW has been expected as an inexpensive, large-capacity backup recording medium substituting for floppy discs or MO discs.
A primary difference between a recorded data signal on a CD-RW and a data signal on a conventional CD-ROM (reflectivity of more than approximately 60%) is only that the reflectivity is lower by approximately 15 to 25%, and if the existing drive is designed to handle a low reflectivity, then the compatibility is achievable in a wide range. In fact, many CD-ROM drives have already handled it.
In addition, Japanese Laid-Open (Kokai) No. HEI 11-250522 (which sometimes will be referred to hereinafter as a “well-known document”) discloses a technique about a hybrid structure including a non-rewritable aluminum reflection area and a rewritable phase change reflection area. According to the technique disclosed in this well-known document, a non-rewritable recording area, which inhibits rewrite and erase through the use of a dedicated format, is provided in a CD-RW medium while the remaining area is used as a rewritable recording area so that, for read and write, a dedicated CD-RW drive is employed which is capable of restricting write/read by the format dedicated to the non-rewritable recording area.
Still additionally, a large number of drives each capable of recording on both the CD-R and CD-RW media (also capable of rewriting on the CD-RW) have been designed on the basis of the CD-R drive developed prior to the CD-RW, and put on the market.
Rewritable type discs (Partial ROM, P-ROM) having a read only (ROM) area in a section of its information recording area are preferable because of enabling both data distribution and user data recording, and the CD family is likewise required to realize them.
So far, as a write-once type compact disc (CD-R) or rewritable type compact disc (CD-RW), there has been proposed a disc (hybrid disc) in which, through the use of a multisession format, only a first session is used for ROM data while a second session and sessions subsequent thereto are used as a recordable partial ROM area.
However, for the recording of data in the form of fixed-length packets through the use of a format other than the multisession, there is no rule for when specific packets are employed as a ROM area.
Moreover, in the case of the hybrid disc, since the multisession format prescribed or defined originally for the CD-R is directly used for the CD-RW, considerations are also given to only the recordable function with respect to the second session forming a rewritable (RAM) area and subsequent sessions.
For this reason, there arises a need to realize a ROM/RAM-mixed disc (Partial ROM, P-ROM disc), which has a ROM area comprising a pre-pits row and freely rewritable RAM area, by the use of the CD-RW.
With such a ROM/RAM-mixed disc, there is a need to read out data from the ROM area and the RAM area without use of separate readout circuits, and there is a need to inhibit substantial distinction from the readout system side.
Meanwhile, in the recording, the writing in the ROM area is impossible while the recorded data in the RAM area is rewritten by overwrite; therefore, there is a need to distinctively deal with both the data in at least a recording system.
As a conventional example, among magneto-optical discs, there exists a disc having a ROM area comprising a pre-pits row partially. The ROM area is coated as a reflective layer with a recording medium identical to that of the RAM area. However, in the case of the magneto-optical medium, the readout of data originally comprising a pre-pits row involves detection of variation in reflectivity strength while the detection of a magneto-optical signal involving detection of variation in polarization through a complex polarization optical system. That is, since a readout optical system achieves easy distinction, a characteristic exists that, even if a magneto-optical signal is recorded in a pre-pits row by mistake, this does not affect a signal readout system at all, thus preventing destruction of the ROM data.
In the meantime, also for a phase change medium, in view of manufacturing, it is also preferable that the ROM/RAM areas have the same multilayer structure. However, since the readout signal from the ROM area comprising a pre-pits row and the readout signal from the RAM area are obtainable through the use of the same optical system, a phase change recorded signal (physically rewritable signal obtainable by a mark row formed on the basis of the difference in property from a peripheral area in a phase change recording layer), by contrast, is overwritten on the pre-pits row to superimpose a RAM recording signal on the pre-pits data, which can destroy the ROM data.
Currently, although there is an example in which write inhibit is made in units of files on an operating system and the definition of a read only file takes place, the reliability is low because of easy alteration/falsification. No prescription about write inhibit or ROM data attribution exists, as it is, at the logical format level in units of bits or blocks of digital data in lower-order than file attribution.
In the case of a P-ROM disc using a phase change medium, a recording system is required to recognize a ROM area without depending upon an operating system, or to inhibit rewriting in a recorded area and recognize it as a ROM area thereafter. In particular, a phase change type CD-RW disc, prescribed such that an intended read only compact disc and data format/readout signal are the same in physical characteristics, is required to seize a ROM area and a RAM area in a recording system.
Among concrete applications for a P-ROM utilizing a phase change medium, there are textbooks for use in repeated practice of languages or music presented in the form of CDs. In such applications, a sentence of a foreign language or a measure of a music, serving as a model (demonstration), is read out as application data to call upon a user to repeat it, and the user immediately records the repeated contents to put them as new input information in a user data area.
Heretofore, although such an application has been done with a cassette tape, after the demonstration, i.e., readout, a need for complex works exists, such as head search of a tape and switching to readout/recording modes for recording the “repetition”. Although there are some cases using a solid-state memory device instead, since limitation is imposed on the recording capacity, difficulty is experienced in dealing with a large volume of demonstration data for a long period of time. In addition, because of the employment of a high-class compression technique to reduce data volume, a delicate nuance, which is said to be necessary for the practice of languages or music, can drop out from the data. With a capacity of 650 to 700 MB like CD-RW, it is possible to accumulate voice data equivalent in quality to that of CD even with almost no compression, or to further increase the voice data volume through the use of a voice compression technique such as MP3.
The employment of an image compression technique such as JPEG or MPEG1 enables still picture and moving picture demonstrations and recording.
Meanwhile, in general, the demonstration is divided in units of several seconds to several tens seconds in order to facilitate the repetition, and the recording of the demonstration and user data are required to be made repeatedly within a given time length, so there is a need to shorten the time needed for the switching in recording between the demonstration and the user data to the utmost.
Accordingly, if an application program is stored on one CD-RW disc and the program and demonstration data are read out therefrom to conduct the demonstrations and user data involving repeated data is then recorded on the same CD-RW disc, this is extremely convenient, for that recording and readout become feasible with the same recording/readout apparatus.
Moreover, commonly, for such an application, two kinds of data: a main routine comprising an executive program and a demonstration data collection comprising a plurality of contents, are collected as ROM data. For example, here the main routine is such a program as a menu screen appears as an user interface to execute various types of processing according to selection by the user. When the user selects the execution of a specified demonstration in the menu screen, selected data is acquired from the demonstration data collection so that the demonstration is implemented by means of a program of the main routine.
In this case, if the user updates only the demonstration data collection without changing the main routine, discs for the purpose of small-volume many-kind application distribution are producible with high efficiency. In view of the actual circumstance of computer-aided publishing, an extremely urgent and important requirement is that, instead of a simple CD-ROM, small-volume many-kind application discs are produced as ROM data capable of updating partially.
It is an object of the present invention to provide a P-ROM, data recording method, data readout method and data erase method easy to produce and providing less possibility of destruction or falsification of ROM data, and more particularly to provide an optical recording medium, data recording method for rewritable phase change type optical disc, data erase method for rewritable compact disc, data erase method for rewritable phase change type recording medium, read only data erase method, and recording/readout apparatus.
More concretely, the present invention relates to a rewritable compact disc having both a read only area and rewritable area.